The present invention relates to a novel hydraulic drive system for a broadcast spreader.
Spreaders of a type mounted on a truck or similar vehicle are well known for dispensing granular material such as salt or sand on highways and streets or other materials such as fertilizer and limestone on farms. Such spreaders usually include a dispensing mechanism such as one or more spinner discs for throwing the material outwardly and an auger or conveyor for delivering the material from a box or other similar source of supply to the spinner. It has been common practice to drive the spinner and the conveyor by separate hydraulic motors supplied by hydraulic fluid under pressure from a fixed displacement pump driven by the engine of the vehicle. Since the engine speed of the vehicle and therefore the pump speed will vary during operation and since it is frequently desirable to adjust the speeds of either the spinner motor or the conveyor motor, or both, the volume of hydraulic fluid under pressure actually required to operate the motors varies widely with respect to the fluid actually delivered by the pump. Thus, it has been common practice to utilize a pressure compensated bypass flow regulator valve so that excess fluid delivered by the pump is directed back to the pump reservoir.
With hydraulic systems of the type heretofore contemplated for such spreader apparatus, the fact is that there is practically always a significant surplus of fluid or oil being pumped and being dumped back to the reservoir and this results in undesirable oil heating. As a result, it has been necessary to utilize relatively large hydraulic reservoirs, radiators and the like in order to accommodate or eliminate oil overheating.
It is an important object of the present invention to provide a novel hydraulic drive system for a plurality of components such as spinners and conveyors in a spreader whereby heat problems are substantially reduced or eliminated and hydraulic system efficiency is greatly improved.
A further more specific object of the present invention is to provide a novel hydraulic system of the above described type wherein the volume of hydraulic fluid actually pumped is varied in accordance with the needs of the workload whereby pumping of excess fluid is substantially eliminated.
Other objects of the present invention are to provide a novel hydraulic system of the above described type which is of relatively simple and economical construction, is easy to install and has improved reliability.
Other objects and advantages of the present invention will become apparent from the following description and the accompanying drawings wherein like reference numerals are used throughout to indicate similar elements and components.